ricin B-type lectin domain, beta-trefoil fold, found in Streptomyces olivaceoviridis endo-1,4-beta-xylanase and similar proteins
The family includes Streptomyces olivaceoviridis endo-1,4-beta-xylanase (XLN, EC 3.2.1.8), Streptomyces avermitilis beta-L-arabinopyranosidase (EC 3.2.1.185), and Streptomyces coelicolor extracellular exo-alpha-L-arabinofuranosidase (ABF, EC 3.2.1.55). XLN, also called xylanase, or 1,4-beta-D-xylan xylanohydrolase, belongs to the glycosyl hydrolase 10 (cellulase F) family. It contributes to hydrolyze hemicellulose, the major component of plant cell walls. XLN contains a (beta/alpha)8-barrel as a catalytic domain, a family 13 carbohydrate binding module (CBM13) as a xylan binding domain (XBD) and a Gly/Pro-rich linker between them. Beta-L-arabinopyranosidase belongs to the glycosyl hydrolase 27 (GH27) family. It has a GH27 catalytic domain, an antiparallel beta-domain containing Greek key motifs, another antiparallel beta-domain forming a jellyroll structure, and a CBM13 module. ScAraf62A, also called ABF, or arabinosidase, or arabinoxylan arabinofuranohydrolase, belongs to the glycosyl hydrolase 62 (GH62) family. It is involved in the degradation of xylan and is a key enzyme in the complete degradation of the plant cell wall. It has a specific arabinofuranose-debranching activity on xylan from gramineae. It acts synergistically with xylanases and binds specifically to xylan. ScAraf62A comprises a CBM13 module at its N-terminus and a catalytic domain at its C-terminus. This model corresponds to the CBM13 module, which is a ricin B-type lectin domain with a beta-trefoil fold, characterized by 12 beta strands folded into three similar trefoil subdomains (alpha, beta, and gamma) associated to give an overall structure with pseudo-3-fold symmetry. Each subdomain may contain a potential sugar-binding pocket.
Jiyao W et al.(2023). "The conserved domain database in 2023.",